For example, Patent Document 1 discloses a valve device equipped to an internal combustion engine, which is equipped with a turbocharger in an intake and exhaust system. The valve device of Patent Document 1 includes a low-pressure EGR valve and a valve angle sensor. The low-pressure EGR valve opens and closes a low-pressure EGR passage. The valve angle sensor sends an electric signal according to an angle of the low-pressure EGR valve.
A conventional method for setting an output characteristic of a valve angle sensor employs following processes. Specifically, an output value at the mechanical full close position, which is a full close position in a mechanical configuration, is set. Further, an output value at the mechanical full open position, which is a full open position in a mechanical configuration, is set. The output characteristic is obtained as an angle to output value relation, which is linearly interpolated.
More specifically, a value is written in the valve angle sensor, such that the valve angle sensor outputs a predetermined voltage Vc at the mechanical full close position. In addition, a value is written in the valve angle sensor, such that the valve angle sensor outputs a predetermined voltage Vo at the mechanical full open position.
(Patent Document 1)
Publication of Unexamined Japanese Patent Application No. 2011-32929
In general, a rotation angle (actual angle) of a valve at the mechanical full open position may vary for each product. Therefore, in the conventional method, an output characteristic of a valve angle sensor may vary for each product. Details will be described with reference to FIG. 7.
For example, it is supposed that the actual angle is ideally 0 deg at the mechanical full close position, and the actual angle is ideally θo at the mechanical full open position. Nevertheless, in reality, the actual angle varies from the supposed angle at the mechanical full close position or at the mechanical full open position, due to a dimensional error and/or the like. In the present assumption, for a product A, the actual angle is θa, which is less than θo, at the mechanical full open position. In addition, for a product B, the actual angle is θb, which is greater than θo, at the mechanical full open position.
In this case, when the value is written in the valve angle sensor, such that the output value at the mechanical full open position becomes Vo uniformly, the output characteristics of both the product A and the product B are away from the ideal characteristic, as shown in FIG. 7. Accordingly, an output characteristic may vary for each product.